1. Field of the Invention
This invention relates to an improvement in a process to produce by a combination of propane and pentane deasphalting an oil of a specified quality from a bituminous material that would otherwise by unobtainable in the same yield by pentane or propane deasphalting processes alone, or in the alternative, to produce a higher yield of comparable quality oil from the bituminous material.
2. Brief Description of the Prior Art
Many methods of extracting bituminous materials have been disclosed previously in the art, perhaps the most well-known of these being propane extraction in which asphaltic materials are recovered from bituminous materials such as reduced crudes by means of a single-solvent extraction. In such extraction, plugging of the extraction equipment may occur in the section between the point of introduction of the propane, thereby making continuous operation difficult.
It has been recognized that the tendency toward plugging in conventional propane deasphalting installations increases with an increase in the concentration of the asphaltenes in the bituminous material. Therefore, this tendency toward plugging acts as a direct limit on the yield of high quality oil product that may be extracted from the bituminous material and successfully separated from the asphaltic product. Any attempt to increase this yield results in a decrease in quality of the oil product that may be extracted from the bituminous material and successfully separated from the asphaltic product. The decrease in quality of the oil product is due to a failure to completely separate it from the asphaltic product.
U.S. Pat. No. 3,053,751 suggests that the plugging problem may be overcome through the utilization of elevated temperatures and pressures. However, the imposition of such new conditions in existing installations presupposes that such installations are capable of operating at pressures higher than those for which they were originally designed or at which they originally functioned.
U.S. Pat. No. 2,500,757 discloses a deasphalting process which requires at least three stages. A liquefied normally gaseous hydrocarbon is mixed with the feed and introduced into a first separation zone maintained at a first temperature level. The feed is separated into a resin-oil phase and an asphaltic phase. The resin-oil phase is removed and introduced into a second separation zone maintained at a second temperature level to separate the resin-oil phase into a resin phase and an oil phase. The oil phase is recovered as product and the resin phase is recycled to the first separation zone. The asphaltic phase is removed from the first separation zone and mixed with additional solvent. It then is introduced into a third separation zone maintained at a third temperature level and allowed to separate into additional oil and asphaltic phases. The oil phase is recycled to the first separation zone and the asphaltic phase is removed and mixed with still more additional solvent before introduction into a fourth separation zone. In the fourth separation zone, maintained at a fourth temperature level, the asphaltic phase separates into a substantially deoiled asphalt phase and an oil phase. The oil phase then is recycled to the third separation zone. The disadvantages of this process are the number of separation zones required, the many different temperature levels which must be maintained and the necessity of adding additional solvent to the separated asphaltic phase entering subsequent separation zones.
U.S. Pat. No. 2,940,920 discloses that solvents other than the light hydrocarbons in the C.sub.2 to C.sub.4 range may be used to separate a bituminous material into at least two fractions at a greatly improved rate of separation and in a manner which eliminates certain prior art operating difficulties encountered in the use of propane-type solvents. Such patent discloses effectuating the separation through the utilization of high temperature-pressure techniques and pentane as one of a group of suitable solvents. The use of that method of separation permits a deeper cut to be made in the bituminous material, but as a consequence, more resinous bodies are present in the oil fraction which tend to decrease the quality of said oil.
Thus, the pentane process (U.S. Pat. No. 2,940,920) alone will produce an oil product in increased yields over propane deasphalting processes but not at a comparable quality, the pentane extracted oil product being heavier and darker by virtue of contained resins from which it was separated in the last phase of the pentane process. This small quantity of resinous bodies results in an oil product that is higher in carbon residue, in sulfur, and most importantly, in metals. In this condition, the oil product is not as suitable as most solvent refined oils either for catalytic cracking charge due to its high metals content or for lubricating stock manufacture because of its resinous bodies content.